Re: Gallery all of a sudden very laggy

@Ciralias  Funny you should mention Avast.  A couple of the errors in your dxdiag list notificationcontroller.dll; these errors seem to often be related to an issue with Avast.  Before uninstalling it, you could try one approach that appears to have worked for other people:

• Open the Start menu, and select Settings
• Click System > Apps and Features, and find Avast on the list
• Select Modify, then uncheck do not disturb
• Restart your computer and test.  To keep things simple, try another clean boot first.

I don't have Avast myself, so I can't check whether this setting is accessible.  If not, you can try temporarily deactivating Avast, just to confirm that it's the source of your lag.  Here's how to disable "core shields":

https://support.avast.com/en-eu/article/Antivirus-shield-settings